CommentaryH5N1
Transmission in Clusters Is Not Limited to Blood Relatives

Recombinomics
CommentaryMay 29, 2006So far, scientists think, all such case
have involved passing the virus between blood relatives. Some experts
theorize that may mean some people have a genetic susceptibility to the
disease, but there is no evidence to support that.

The above comments, indicating that all H5N1 bird flu transmissions in
clustwers are between blood relatives, are false. There are several
examples of H5N1 confirmation in cluster members that are not blood
relatives. In 2005 the largest familial cluster was in a family
of five in Haiphong. All five family members were
hospitalized on the same day and all were H5N1 confirmed. The
family consisted of a mother, father, and three daughters, so
transmission was not limited to blood relatives.

Similarly, in 2005 there was a cluster involving a pair of siblings and
the nurse
of the index case. The nurse was not a blood relative
and had no exposure to poultry.

More recently there was a large cluster in Azerbaijain involving
siblings and a close
friend who was also not a blood relative.

Since most family members are blood relatives, most infected in
familial clusters will be blood relatives, but these are the people who
are in close contact with infected family members. The close
contact is a major driver of these infections, which are largely
limited to family members.

In the Azerbaijan cluster, all confirmed cases were siblings.
There was no reported transmission to either parent. Similarly
the large cluster of confirmed cases in Turkey
also involved siblings. There was no confirmed transmission to
either parent. Thus, even though both parents were blood
relatives to the siblings, none were confirmed to have been infected.

Although most family members are blood relatives and all members of the
Sumatra cluster were blood relatives, the exceptions cited above weaken
evidence to support a genetic susceptibility as a major driver of
familial clusters.
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